The Sony Alpha SLT-A77 vies with professional digital SLRs from the company’s rivals, offering a whopping resolution of 24.3 megapixels from an Exmor APS HD CMOS image sensor. Coupled with Sony’s latest-generation Bionz image processor, this offers the ability to capture a whopping twelve full-resolution frames per second with a fixed aperture, leading Sony to describe the the A77 as being the world’s fastest APS-C interchangeable-lens camera. Even with a variable aperture, the A77 offers a very swift eight frames per second. The A77’s solid, weather-sealed magnesium alloy body also includes a new LCD articulation mechanism that allows viewing from in front of the camera, even when mounted on a tripod.

Another key point of the new design is its new Organic LED electronic viewfinder, which offers a staggering 2.4 million RGB dots of resolution. There’s also a new 19-point autofocus sensor with 11 cross-type points, 1,200 zone metering, shutter speeds to 1/8,000 second, and ISO sensitivity ranging from 50 to 16,000 equivalents. The Sony A77 also offers the ability to capture Full HD video at 60 progressive-scan frames per second, from 60 fps sensor data, another world’s first for an interchangeable lens camera, says Sony. As you’d expect for an SLT-series camera, the A77 offers full-time phase detection autofocus during video capture, a unique selling point of Sony’s Translucent Mirror design. Full manual and priority exposure control is possible during movie capture.

Alongside the camera body, Sony has unveiled a new weather-sealed zoom lens, the Sony DT 16-50mm F2.8 SSM. There’s also a new portrait / battery grip designed for the A77 body, the VG-C77AM vertical grip, and again weather-sealed. (Together with the existing HVL-F43AM flash strobe, this brings together the possibility of a completely sealed system, although the remainder of Sony’s lens lineup isn’t currently sealed.)

The Sony SLT-A77 should be available in the US market from October 2011. Body-only pricing is set at approximately US$1,400, while a kit version including the Sony DT 16-50mm F2.8 SSM standard zoom lens will be priced at around US$2,000. (The lens itself will also be available separately a few weeks after the A77’s launch, priced at around $700 by itself.) The VG-C77AM vertical grip will be available in October, and cost about US$300.

It is the A77’s high speed shooting modes which have grabbed the most attention, but again, we find ourselves celebrating other, less flashy aspects of the camera’s feature set. Its excellent EVF, versatile and intuitive live view and AF system, and its solid, reassuringly well thought-out operational ergonomics are all better reasons to buy this camera.

Overall the A77 is a logical, and successful upgrade to the pioneering A55, and one that should make a lot of enthusiast photographers very happy. If you’re interested in the A77 as a sports and fast-action camera though, don’t be blinded by its fast framerates alone. The A77 is very good, but in our experience the more conventional Canon EOS 7D and Nikon D7000 both offer slightly more reliable AF tracking and framerates which although slower than 12fps, are still plenty fast enough for most applications.

After a four-year wait, Sony has returned to the enthusiast/semi-pro end of the DSLR market. Having made little impact in that market with the A700 that very closely resembled the conventional DSLRs made by Canon and Nikon, Sony has spent the intervening time developing something a bit different. The A77 builds on the company’s ‘translucent mirror’ technology, and uses an electronic rather than optical viewfinder. The final result is a product that may look traditional, but is able to promise the unconventional.

Making a major leap in the camera market, the Sony A77 reaches into pro territory, able to capture 12 frames per second with a 24.3-megapixel camera that feels great and handles like your typical enthusiast digital SLR. Its optional 16-50mm kit lens also delivers excellent quality for the money.

A900 or A77? A tough call. The A900 currently sells for some $2,700; a full $1,200 dollars more than the new A77. The A77 is weatherproof, has higher frame rates, GPS, electronic level, an articulated LCD, and a built in flash. The A900 has one of the world’s best (and maybe last) large and bright reflex prism viewfinders. Like I said – a tough call.